2^x - 9*3^y = 7
2^x - 3^y = 8/9
2^x = 7 + 9*3^y
2^x = 8/9 + 3^y
---
7 + 9*3^y = 8/9 + 3^y
9*3^y - 3^y = 8/9 - 7
8*3^y = - 6 1/9
Слева > 0 справа < 0
решений нет
2^x - 9*3^y = 7
2^x - 3^y = 8/9
2^x = 7 + 9*3^y
2^x = 8/9 + 3^y
---
7 + 9*3^y = 8/9 + 3^y
9*3^y - 3^y = 8/9 - 7
8*3^y = - 6 1/9
Слева > 0 справа < 0
решений нет